Proto is a framework for building Domain Specific Embedded Languages in C++.
It provides tools for constructing, type-checking, transforming and executing
expression templates[2]
. More specifically, Proto provides:

An expression tree data structure.

A mechanism for giving expressions additional behaviors and members.

Operator overloads for building the tree from an expression.

Utilities for defining the grammar to which an expression must conform.

An extensible mechanism for immediately executing an expression template.

An extensible set of tree transformations to apply to expression trees.

Expression Templates are an advanced technique that C++ library developers
use to define embedded mini-languages that target specific problem domains.
The technique has been used to create efficient and easy-to-use libraries for
linear algebra as well as to define C++ parser generators with a readable syntax.
But developing such a library involves writing an inordinate amount of unreadable
and unmaintainable template mumbo-jumbo. Boost.Proto eases the development
of domain-specific embedded
languages (DSELs). Use Proto to define the primitives of your mini-language
and let Proto handle the operator overloading and the construction of the expression
parse tree. Immediately evaluate the expression tree by passing it a function
object. Or transform the expression tree by defining the grammar of your mini-language,
decorated with an assortment of tree transforms provided by Proto or defined
by you. Then use the grammar to give your users short and readable syntax errors
for invalid expressions! No more mumbo-jumbo -- an expression template library
developed with Proto is declarative and readable.

This documentation makes use of the following naming and formatting conventions.

Code is in fixedwidthfont and is syntax-highlighted.

Replaceable text that you will need to supply is in
italics
.

If a name refers to a free function, it is specified like this: free_function();
that is, it is in code font and its name is followed by ()
to indicate that it is a free function.

If a name refers to a class template, it is specified like this: class_template<>;
that is, it is in code font and its name is followed by <>
to indicate that it is a class template.

If a name refers to a function-like macro, it is specified like this: MACRO();
that is, it is uppercase in code font and its name is followed by () to indicate that it is a function-like
macro. Object-like macros appear without the trailing ().

Names that refer to concepts in the generic programming
sense are specified in CamelCase.

Note

In addition, notes such as this one specify non-essential information that
provides additional background or rationale.

Finally, you can mentally add the following to any code fragments in this document:

// Include all of Proto
#include<boost/proto/proto.hpp>// Create some namespace aliases
namespacempl=boost::mpl;namespacefusion=boost::fusion;namespaceproto=boost::proto;// Allow unqualified use of Proto's wildcard pattern
usingproto::_;